2. Prior Art
This invention relates to a solid waste communiting apparatus. Such devices have been established in the art and are now widely used in a variety of industrial applications, such as municipal waste treatment and industrial applications. Reference is made to U.S. Pat. No. 4,046,324, which discloses such a basic system that has achieved commercial success.
By definition, comminution is the reduction of particle size of solid waste material to minute particles. It is generally performed by shearing, shredding and crushing of the waste material. As set forth in the ""324 patent, comminution occurs by utilizing a pair of counter-rotating intermeshed cutting members.
The solid waste material is fed into the interface between cutting elements, typically utilizing a fluid carrier medium and shearing action occurs because the two cutters overlap each other such that opposing forces of counter-rotation of the cutting elements on the different stacks act on the solid material as it passes through the device.
In practice, such devices are generally used in an influent/effluent path. That is, the solid material is generally entrained in a liquid and the device is placed directly in the liquid stream. By having the solid material entrained in a liquid stream transportation of the material to and from the unit occurs. Further, by softening the solid particles, a greater degree of comminution is achieved. Devices of the type disclosed in the ""324 patent have found commercial success and are widely used in waste treatment facilities, shipboard use and the like. As can be appreciated, the environment of use is very harsh for the equipment and as such, routine maintenance is required in both a preventative sense and also to immediately repair breakdowns when they occur thus minimizing system down-time.
An important aspect of such maintenance and repair is the integrity of the seals which provide the cutter stacks to rotate while minimizing friction. Given the mass of the cutter stacks together with high motor torque, loads on the seals are large and thus seal integrity is a primary consideration. In the past, two-shafted machines such as the ""324 device required that the seal assembly be an integral part of the device. Such is illustrated in FIG. 1 of the ""324 patent. As a result, if there was a seal failure other critical components of the device were likely to be effected. This failure of a seal could thus mean that bearings could fail and seize up the cutter stack.
Importantly, to repair the seal assembly, in the prior art, there was a requirement that the device be disassembled and completely reassembled. In the context of a unit which is used in fluid waste treatment that down-time, in some cases as long as a day could have detrimental effects in the ability of a plant to process waste. Such would require rerouting solid waste, shutting down a portion of the facility and otherwise result in an inefficient operation.
Moreover, in prior art two-shafted machines, the cutter stack and the various seal components were integral and in-line with a fixed geometry. Consequently, tightening of the cutter stack, by compression, resulted in compression of the seals. Again, such is illustrated in FIG. 1 of the ""324 patent. It has been recognized however, that under normal operating conditions the cutter thickness experiences wear and thus the overall thickness of the stack tends to reduce over time. The result is an effective reduction in the overall stack height and the stack therefore tends to become loose. As a consequence, initial compression of various seal components is lost and the seal faces tend to separate. The result is leakage across the seal with the subsequent result of bearing failure.
Another deficiency in the prior art was the use of a labyrinth between the main fluid chamber and the seal faces. The labyrinth was generally incorporated into the seal components as sacrificial component. Because such devices are used in applications which include a high grit content, the labyrinth tended to be a relatively high wear component. As a consequence, seal components had to be removed to replace the labyrinth with the potential for seal damage upon reassembly.
Given these deficiencies in the prior art, it is an object of this invention to provide an improved solid waste comminutor that overcomes the operational and assembly problems of prior devices in terms of access to components.
It is a further object of this invention to provide a solid waste comminutor which employs a cartridge with a balanced seal-bearing design to produce a constant seal face pressure.
A further object of this invention is to provide a solid waste comminutor of improved seal and bearing life by improved seal effectiveness which is independent of stack tightness.
Yet another object of this invention is to provide a seal cartridge for a solid waste comminutor which has an independent labyrinth that can be replaced without disassembly of the seal-bearing structure.
Another object of this invention is to provide an improved solid waste comminutor that utilizes an improved side rail assembly to direct flow through the comminutor.
A still further object of this invention is to provide an improved solid waste comminutor that employs an access port at the top of the cutter stack to permit stack tightening and a reduction in the size of the lower compartment to reduce head drop.
These and other objects of this invention are achieved by a dual stack solid waste comminutor having preassembled bearing-sealing elements that are replaceable individually. That modular assembly improves system life while minimizing down-time. In accordance with this invention a cartridge type seal is employed utilizing two modular assemblies, one on each end of the cutter stack. Each of the modular bearing-seal assemblies comprises a pair of identical bearing-seal cartridges. Two identical bearing-seal cartridges are assembled into the end housing to thus form top and bottom modular pairs.
Further, in accordance with this invention the bearing-seal cartridges float within the housing to provide movement with shaft movement thereby reducing the stress on the shafts and bearings.
A quick exchange of the mechanical subassembly, which includes bearings, O-ring seals and cartridge housing itself can be effectuated. As a result of this modular assembly, an individual seal cartridge can be installed quickly without the need to disassemble the entire subassembly.
Another advantage of this technique is that the bearing-seal cartridge is identical for the top and bottom of the cutter stack. As a consequence, a deficiency in the prior art which used two different assemblies has been eliminated. The bearing-seal cartridge is an item which is preassembled and installed as received. Thus, there is no requirement that the individual items, the various races, bearings and the like be assembled at the job site. Rather, the cartridge is interchangeable as a unit and is inserted into the end housing.
Further, in accordance with this invention re-torquoring of the cutter stack can be accomplished while the unit is still in-channel and installed. This is accomplished by an access port located at the top of the cutter stack assembly. It has been demonstrated that in practice, the most common preventative maintenance function is re-torquing the cutter stack to maintain stack compression for maximum cutting efficiency.
Prior to this invention a loss of stack compressibility leads directly to premature seal and bearing failure, primarily of the bottom seal assembly. In accordance with this invention, the tightness of the seal assembly is independent of total stack height, since it is designed as a self contained unit no disassembly is required.
Another advantage of this invention is an early warning seal failure detection system which can be used to prevent premature bearing failure. The invention provides for a drain port and/or weep holes in the shafts that allow fluid permeating from the seal to escape to the exterior. This can thus be viewed by maintenance personnel during routine checks of the system.
Additionally, this invention uses an improved side rail system to both strengthen the device as well as direct flow around and toward the cutter elements. The side rails have a greater strength compared to normal unit side plates and thus provide additional stiffness for the device. The two side rails function to channel the flow at the input side of the device into the cutters. At the periphery of the cutter and on the downstream side, the side rails accelerate the flow to promote cleaning of the cutter elements.
These and other objects of this invention will become apparent by a review of the attached drawing and the description of the preferred embodiment which follows.